Biodiversity in NSW continues to face mounting pressure from landscape fragmentation and disturbance. Since European colonisation, 54% of forests and woodlands in NSW have been destroyed, amounting to over 60% of the state’s forest estate being degraded. Habitat loss drives significant changes to community composition, species interactions and ecosystem function, including declines in population density and species richness. Fragmented populations are also more vulnerable to threats including fire, predation and disease, raising the likelihood of localised extinction. Ensuring connectivity between these fragmented landscapes is one way these negative effects can be mitigated. Previous research published in the Journal of Mammalogy found that continuous eucalypt forest supported more species than isolated patches, and these species are more resilient to disturbances. In addition, connectivity also supports a broad variety of ecosystem services, including pollination and seed dispersal.
Cawley’s Bridge Wildlife Corridor
An example of an innovative wildlife connectivity initiative within NSW is the Cawley’s Bridge wildlife corridor which passes across the M1 Princes Highway, south of Sydney. Five decades since the concept’s inception, the Cawley’s Bridge project is the first known retrofit of existing infrastructure for use as a wildlife corridor in Australia. Cawley’s Bridge is a small bridge across the M1 Highway which has been largely unused since the 1970s. Located just south of Waterfall, it connects the Royal National Park, Garawarra State Conservation Area and Heathcote National Park, relatively small yet vital conservation reserves located on the urban fringes of Sydney. Surrounding habitat is being cleared at an increasing rate, isolating the reserves and creating barriers to wildlife movement. By connecting the parks and restoring habitat connectivity, species are safeguarded against the many threats of a fragmented landscape, and their populations are able to disperse across the landscape. Specifically, there is hope that the bridge will allow koala (Phascolarctos cinereus) populations in Heathcote National Park to expand eastward.
Koala Populations in Southern Sydney
A previously undiscovered colony of over 190 koalas in Heathcote National Park was identified in 2021 by two local environmentalists. The discovery of a large, chlamydia free and actively breeding population so close to Sydney is a significant discovery, as in February 2022 koala populations in NSW, QLD & ACT were listed as endangered under the Environment Protection and Biodiversity Conservation Act (EPBC Act) 1990. However, the fragmented location of this colony on the urban fringes of Sydney places it at high risk for various threats, including fire, predation, car strikes and disease.
Despite its proximity to the colony in Heathcote National Park and its identified suitability as koala habitat, the Royal National Park does not have a recorded koala population. NSW BioNet records show less than 10 recorded koala sightings within the park since 2015. In recent years, the fragmented nature of the Royal National Park has been outlined as a major barrier to koala population expansion into the park, as it is bordered by major highways and bodies of water. Another potential explanation for the lack of koalas in the Royal is the short-interval fire regimes the park experienced in the late 90s. Catastrophic fires devastated the Royal National Park in 1994, burning over 95% of vegetation in the park and having a devastating effect on fauna. Further severe fires followed in 2002, raising the possibility that short intervals between severe fire regimes did not allow the koala population in the Royal to recover.
Projects like the Cawley’s Bridge Wildlife Corridor increase the likelihood of the recovery of koala populations within the Royal and will help strengthen population resilience against threats like high severity fire. Major fire events like those in 1994 and 2002 are predicted to increase in frequency under climate change, and increasing landscape connectivity will help reduce the impact on wildlife populations. Increasing connectivity between the reserves will allow species to escape fire fronts, locate refuge in unburnt areas, and then subsequently recolonise burnt areas. Without connectivity, wildlife may become trapped, leading to higher localised extinction rates and slower recovery. Reducing fragmentation between populations will also increase genetic diversity within species, increasing population adaptability and resilience to disease and environmental change.
In a time of increasing development and fragmentation within Greater Sydney, the Cawley’s Bridge project is a vital lifeline for the South Sydney Koala populations, aiming to expand and safeguard their populations for years to come.
The Cawley’s Bridge project is funded by the NSW Department of Climate Change, Energy, the Environment and Water (DCCEEW) and the work is being undertaken by Transport for NSW (TfNSW).
This article was written by Elke Black, Healthy Ecosystems Program Volunteer with the Nature Conservation Council of NSW.
Original story by K. Fuller and R. McDonald for ABC Illawarra here: https://www.abc.net.au/news/2026-02-22/cawleys-bridge-wildlife-crossing-retrofit/106365756
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